Rat supraoptic magnocellular neurones show distinct large conductance, Ca2+-activated K+ channel subtypes in cell bodies versus nerve endings

Alejandro Dopico, Hélène Widmer, Gang Wang, José R. Lemos, Steven N. Treistman

Research output: Contribution to journalArticle

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Abstract

1. Large conductance, Ca2+-activated K+ (BK) channels were identified in freshly dissociated rat supraoptic neurones using patch clamp techniques. 2. The single channel conductance of cell body BK channels, recorded from inside-out patches in symmetric 145 mM K+, was 246.1 pS, compared with 213 pS in nerve ending BK channels (P < 0.01). 3. At low open probability (P(o)), the reciprocal of the slope in the ln(NP(o))-voltage relationship (N, number of available channels in the patch) for cell body and nerve ending channels were similar: 11 vs. 14 mV per e-fold change in NP(o), respectively. 4. At 40 mV, the [Ca2+]1 producing half-maximal activation was 273 nM, as opposed to > 1.53 μM for the neurohypophysial channel, indicating the higher Ca2+ sensitivity of the cell body isochannel. 5. Cell body BK channels showed fast kinetics (open time constant, 8.5 ms; fast closed time constant, 1.6 and slow closed time constant, 12.7 ms), identifying them as 'type I' isochannels, as opposed to the slow gating (type II) of neurohypophysial BK channels. 6. Cell body BK activity was reduced 10 nM charybdotoxin (NP(o), 37% of control), or 10 nM iberiotoxin (NP(o), 5% of control), whereas neurohypophysial BK channels are insensitive to charybdotoxin at concentrations as high as 360 nM. 7. Whilst blockade of nerve ending BK channels markedly slowed the repolarization of evoked single spikes, blockade of cell body channels was without effect on repolarization of evoked single spikes. 8. Ethanol reversibly increased neurohypophysial BK channel activity (EC50, 22 mM; maximal effect, 100 mM). In contrast, ethanol (up to 100 mM) failed to increase cell body BK channel activity. 9. In conclusion, we have characterized BK channels in supraoptic neuronal cell bodies, and demonstrated that they display different electrophysiological and pharmacological properties from their counterparts in the nerve endings.

Original languageEnglish (US)
Pages (from-to)101-114
Number of pages14
JournalJournal of Physiology
Volume519
Issue number1
DOIs
StatePublished - Aug 15 1999

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Large-Conductance Calcium-Activated Potassium Channels
Calcium-Activated Potassium Channels
Nerve Endings
Neurons
Charybdotoxin
Ethanol
Cell Body
Patch-Clamp Techniques
Pharmacology

All Science Journal Classification (ASJC) codes

  • Physiology

Cite this

Rat supraoptic magnocellular neurones show distinct large conductance, Ca2+-activated K+ channel subtypes in cell bodies versus nerve endings. / Dopico, Alejandro; Widmer, Hélène; Wang, Gang; Lemos, José R.; Treistman, Steven N.

In: Journal of Physiology, Vol. 519, No. 1, 15.08.1999, p. 101-114.

Research output: Contribution to journalArticle

Dopico, Alejandro ; Widmer, Hélène ; Wang, Gang ; Lemos, José R. ; Treistman, Steven N. / Rat supraoptic magnocellular neurones show distinct large conductance, Ca2+-activated K+ channel subtypes in cell bodies versus nerve endings. In: Journal of Physiology. 1999 ; Vol. 519, No. 1. pp. 101-114.
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N2 - 1. Large conductance, Ca2+-activated K+ (BK) channels were identified in freshly dissociated rat supraoptic neurones using patch clamp techniques. 2. The single channel conductance of cell body BK channels, recorded from inside-out patches in symmetric 145 mM K+, was 246.1 pS, compared with 213 pS in nerve ending BK channels (P < 0.01). 3. At low open probability (P(o)), the reciprocal of the slope in the ln(NP(o))-voltage relationship (N, number of available channels in the patch) for cell body and nerve ending channels were similar: 11 vs. 14 mV per e-fold change in NP(o), respectively. 4. At 40 mV, the [Ca2+]1 producing half-maximal activation was 273 nM, as opposed to > 1.53 μM for the neurohypophysial channel, indicating the higher Ca2+ sensitivity of the cell body isochannel. 5. Cell body BK channels showed fast kinetics (open time constant, 8.5 ms; fast closed time constant, 1.6 and slow closed time constant, 12.7 ms), identifying them as 'type I' isochannels, as opposed to the slow gating (type II) of neurohypophysial BK channels. 6. Cell body BK activity was reduced 10 nM charybdotoxin (NP(o), 37% of control), or 10 nM iberiotoxin (NP(o), 5% of control), whereas neurohypophysial BK channels are insensitive to charybdotoxin at concentrations as high as 360 nM. 7. Whilst blockade of nerve ending BK channels markedly slowed the repolarization of evoked single spikes, blockade of cell body channels was without effect on repolarization of evoked single spikes. 8. Ethanol reversibly increased neurohypophysial BK channel activity (EC50, 22 mM; maximal effect, 100 mM). In contrast, ethanol (up to 100 mM) failed to increase cell body BK channel activity. 9. In conclusion, we have characterized BK channels in supraoptic neuronal cell bodies, and demonstrated that they display different electrophysiological and pharmacological properties from their counterparts in the nerve endings.

AB - 1. Large conductance, Ca2+-activated K+ (BK) channels were identified in freshly dissociated rat supraoptic neurones using patch clamp techniques. 2. The single channel conductance of cell body BK channels, recorded from inside-out patches in symmetric 145 mM K+, was 246.1 pS, compared with 213 pS in nerve ending BK channels (P < 0.01). 3. At low open probability (P(o)), the reciprocal of the slope in the ln(NP(o))-voltage relationship (N, number of available channels in the patch) for cell body and nerve ending channels were similar: 11 vs. 14 mV per e-fold change in NP(o), respectively. 4. At 40 mV, the [Ca2+]1 producing half-maximal activation was 273 nM, as opposed to > 1.53 μM for the neurohypophysial channel, indicating the higher Ca2+ sensitivity of the cell body isochannel. 5. Cell body BK channels showed fast kinetics (open time constant, 8.5 ms; fast closed time constant, 1.6 and slow closed time constant, 12.7 ms), identifying them as 'type I' isochannels, as opposed to the slow gating (type II) of neurohypophysial BK channels. 6. Cell body BK activity was reduced 10 nM charybdotoxin (NP(o), 37% of control), or 10 nM iberiotoxin (NP(o), 5% of control), whereas neurohypophysial BK channels are insensitive to charybdotoxin at concentrations as high as 360 nM. 7. Whilst blockade of nerve ending BK channels markedly slowed the repolarization of evoked single spikes, blockade of cell body channels was without effect on repolarization of evoked single spikes. 8. Ethanol reversibly increased neurohypophysial BK channel activity (EC50, 22 mM; maximal effect, 100 mM). In contrast, ethanol (up to 100 mM) failed to increase cell body BK channel activity. 9. In conclusion, we have characterized BK channels in supraoptic neuronal cell bodies, and demonstrated that they display different electrophysiological and pharmacological properties from their counterparts in the nerve endings.

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